The sci.astro FAQ


sci.astro is a newsgroup devoted to the discussion of the science of astronomy. As such its content ranges from the Earth to the farthest reaches of the Universe.

However, certain questions tend to appear fairly regularly. This document attempts to summarize answers to these questions.

This document is posted on the first and third Wednesdays of each month to the newsgroup sci.astro. It is available via anonymous ftp, and it is on the World Wide Web at the sci.astro FAQ site and Internet FAQ Archives. A partial list of worldwide mirrors (both ftp and Web) is also available. (As a general note, many other FAQs are also available from

Questions/comments/flames should be directed to the FAQ maintainer, Joseph Lazio <>.

Table of Contents

Dates in brackets are last edit.

Part A: The Internet and other information sources

  1. What are the sci.astro* newsgroups about? [1999-11-03]

  2. How do I subscribe to sci.astro*? [1998-02-28]

  3. What are the guidelines for posting on astronomy (sci.astro*) newsgroups? [2003-09-18]

  4. What should I do if I see an article that doesn't follow these guidelines? (What about cranks?) [1997-02-04]

  5. Can I get help on my homework from the Net? [1995-07-26]

  6. What are good Net sites for astronomy info and images? [2003-04-27]

  7. How can I find contact addresses for astronomers/observatories? [1996-12-04]

  8. Which observatories offer tours or public viewing? [1995-09-17]

  9. Is there a list of astro jokes? [1999-12-15]

  10. What are good books on astronomy (especially for beginners)? [1995-06-27]

  11. Are there other sources of information? [1996-01-24]

  12. How can I find an astronomy club? [1996-01-24]

  13. Where can I find out about public lectures or star parties? [1995-09-17]

Part B: General

  1. What good is astronomy anyway? [1997-08-06]

  2. What are the largest telescopes? [2001-02-04]

  3. What new telescopes/instruments are being built? [2000-01-01]

  4. What is the resolution of a telescope? [1995-08-23]

  5. What's the difference between astronomy and astrology? [1995-08-23]

  6. Is there scientific evidence for/against astrology? [1995-08-23]

  7. What about God and the creation? [1995-08-27]

  8. What kind of telescope should I buy? [2001-01-17]

  9. What are the possessive adjectives for the planets? [1995-12-05]

  10. Are the planets associated with days of the week? [2000-11-12]

  11. Why does the Moon look so big when it's near the horizon? [1997-01-21]

  12. Is it O.K. to look at the Sun or solar eclipses using exposed film? CDs? [1996-11-20]

  13. Can stars be seen in the daytime from the bottom of a tall chimney, a deep well, or deep mine shaft? [1996-06-14]

  14. Why do eggs balance on the equinox? [1996-06-14]

  15. Is the Earth's sky blue because its atmosphere is nitrogen and oxygen? Or could other planets also have blue skies? [1998-02-06]

  16. What are the Lagrange (L) points? [2003-10-18]

  17. Are humans affected psychologically and/or physically by lunar cycles? [2000-06-03]

  18. How do I become an astronomer? What school should I attend? [1996-07-03]

  19. What was the Star of Bethlehem? [2002-05-04]

  20. Is it possible to see the Moon landing sites? [2003-09-18]

Part C: Time, Calendars, and Terrestrial Phenomena

  1. When is 02/01/04? or is there a standard way of writing dates? [2001-12-14]

  2. What are all those different kinds of time? [2002-05-07]

  3. How do I compute astronomical phenomena for my location? [2002-05-04]

  4. What's a Julian date? modified Julian date? [1998-05-06]

  5. Will 2000 be a leap year? [2000-03-17]

  6. When will the new millennium start? [2001-01-01]

  7. Easter:

    1. When is Easter? [2001-08-14]

    2. Can I calculate the date of Easter? [1996-12-11]

  8. What is a "blue moon?" [2001-10-02]

  9. What is the Green Flash (or Green Ray)? [1999-01-01]

  10. Why isn't the earliest Sunrise (and latest Sunset) on the longest day of the year? [2002-01-30]

  11. How do I calculate the phase of the moon? [2001-08-14]

  12. What is the time delivered by a GPS receiver? [2002-05-07]

  13. Why are there two tides a day and not just one? [1999-12-15]

Part D: Astrophysics

  1. Do neutrinos have rest mass? What if they do? [2002-05-04]

  2. Have physical constants changed with time? [1997-02-04]

  3. What is gravity? [1998-11-04]

  4. Does gravity travel at the speed of light? [1998-05-06]

  5. What are gravitational waves? [1997-06-10]

  6. Can gravitational waves be detected? [2000-08-31]

  7. Do gravitational waves travel at the speed of light? [1996-07-03]

  8. Why can't light escape from a black hole? [1995-10-05]

  9. How can gravity escape from a black hole? [1996-01-24]

  10. What are tachyons? Are they real? [1995-10-02]

  11. What are magnetic monopoles? Are they real? [1996-07-03]

  12. What is the temperature in space? [1998-04-14]

  13. Saturn's rings, proto-planetary disks, accretion disks---Why are disks so common? ]99-07-18]

Part E: Sun, Moon, and Planets

  1. How did the solar system form? [2000-07-15]

  2. Has anyone attempted to discern details of the star that went supernova and formed our local group of stars? [2002-05-04]

  3. What is the "Solar Neutrino Problem?" [1997-07-01]

  4. Could the Sun be part of a binary (multiple) star system? [1995-08-27]

  5. When will the Sun die? How? [1995-08-23]

  6. What happens to the planets when the Sun dies? [2000-03-17]

  7. Could the Sun explode? [1995-07-07]

  8. How are solar system objects and features named? [1995-11-29]

  9. Where can I find pictures and planetary data? (ref)

  10. Could Jupiter become a star? [1995-07-07]

  11. Is Pluto a planet? Is Ceres? Is Titan? [1995-08-18]

  12. Additional planets:

    1. What about a planet (Planet X) outside Pluto's orbit? [2000-05-21]

    2. What about a planet inside Mercury's orbit? [1996-11-20]

  13. Won't there be catastrophes when the planets align in the year 2000? [2000-07-15]

  14. Earth-Moon system:

    1. Why doesn't the Moon rotate? [1997-10-01]

    2. Why does the Moon always show the same face to the Earth? [1997-10-01]

    3. Is the Moon moving away from the Earth? (and why is Phobos moving closer to Mars?) [1997-06-04]

    4. What was the origin of the Moon? [1998-11-04]

  15. What's the difference between a solar and lunar eclipse? Where can I find more information about eclipses? [2001-01-17]

  16. What's the Oort Cloud and Kuiper Belt? [1998-02-28]

  17. Asteroid Impacts

    1. What would be the effects of an asteroid impact on the Earth? [1998-04-14]

    2. What can we do about avoiding impacts? [1998-04-14]

  18. What's the difference between meteoroids, meteors, and meteorites? [1998-04-14]

  19. How do we know that meteorites are from the Mars? (or the Moon?) [2002-05-04]

Part F: Extraterrestrial Life

  1. What is life? [1997-09-03]

  2. Life in the Solar System

    1. Is there life on Mars? [1996-09-03]

    2. Is there life in Jupiter (or Saturn)? [1996-09-03]

    3. Is there life on Jupiter's moon, Europa? [1996-09-03]

    4. Life on Titan? [1997-08-06]

  3. What is the Drake equation? [1995-10-04]

  4. What is the Fermi paradox? [1995-12-28]

  5. Could we detect extraterrestrial life? [1999-09-15]

  6. How far away could we detect radio transmissions? [2000-07-19]

  7. What's a Dyson sphere? [1997-06-04]

  8. What is happening with SETI now? [1998-01-31]

  9. Why search for extraterrestrial intelligence using radio? Why not <fill in the blank> method? [2000-01-01]

  10. Why do we assume that other beings must be based on carbon? Why couldn't organisms be based on other substances? [2001-03-20]

  11. Could life occur on an interstellar planet? [2003-04-27]

Part G: Stars

  1. What are all those different kinds of stars?

    1. General overview and main sequence stars [1996-01-02]

    2. White dwarfs [2003-04-27]

    3. Neutron stars [2003-04-27]

    4. Black holes [2003-04-27]

  2. Are there any green stars? [1995-12-28]

  3. What are the biggest and smallest stars? [1995-06-28]

  4. What fraction of stars are in multiple systems? [1995-06-27]

  5. Where can I get stellar data (especially distances)? [2003-05-08]

  6. Which nearby stars might become supernovae? [1995-12-29]

  7. What will happen on Earth if a nearby star explodes? [2000-02-20]

  8. How are stars named? Can I name/buy one? [1995-12-28]

  9. Do other stars have planets?

  10. What happens to the planets when a planetary nebula is formed? Do they get flung out of the solar system? [2002-05-04]

  11. How far away is the farthest star? [1999-01-01]

  12. Do star maps (or galaxy maps) correct for the motions of the stars? [2003-10-18]

Part H: Galaxies, Clusters, and QSOs

  1. How many stars, galaxies, clusters, QSO's etc. in the Universe? [1997-08-06]

  2. Is there dark matter in galaxies? [1997-12-02]

  3. What is the Hubble constant? What is the best value? [1995-07-19]

  4. How are galaxy distances measured? [1995-06-29]

  5. When people speak of galaxies X billion light years away, does this mean they are that far away now or were that far away when the light left them? [1997-08-06]

  6. What are QSO's ("quasars")? [1995-06-29]

  7. Are the QSO's really at their redshift distances? [2003-02-18]

  8. What about apparent faster-than-light motions? [1995-06-29]

  9. What's the Local Group? [1999-05-19]

Part I:Cosmology and the Universe [1998-02-28]

  1. What do we know about the properties of the Universe?

  2. Why do astronomers favor the Big Bang model of the Universe?

  3. Where is the center of the Universe?

  4. What do people mean by an "open," "flat," or "closed" Universe?

  5. If the Universe is expanding, what about me? or the Earth? or the Solar System?

  6. What is inflation?

  7. How can the Big Bang (or inflation) be right? Doesn't it violate the idea that nothing can move faster than light? (Also, can objects expand away from us faster than the speed of light?)

  8. If the Universe is only 10 billion years old, how can we see objects that are now 30 billion light years away? Why isn't the most distant object we can see only 5 billion light years away?

  9. How can the oldest stars in the Universe be older than the Universe?

  10. What is the Universe expanding into?

  11. Are galaxies really moving away from us or is space-time just expanding?

  12. How can the Universe be infinite if it was all concentrated into a point at the Big Bang?

  13. Why haven't the cosmic microwave background photons outrun the galaxies in the Big Bang?

  14. Can the cosmic microwave background be redshifted starlight?

  15. Why is the sky dark at night? (Olbers' paradox) [2001-10-02]

  16. What about objects with discordant redshifts?

  17. Since energy is conserved, where does the energy of redshifted photons go? [1998-12-03]

  18. There are different ways to measure distances in cosmology? [1999-07-06]

T. Joseph W. Lazio